The trade body representing tour operators has warned that expectations of a boost in tourism from the London Olympics may not be met, after unveiling research that suggested previous games had a "toxic" effect on visitor numbers.

The European Tour Operators Association, which held a seminar on the subject today, released research that showed previous hosts had invariably overestimated the number of foreign visitors and the duration of their stay.

The Sydney games in 2000 anticipated 132,000 visitors and received 97,000 for the games period, while Athens hoped for 105,000 per night in 2004 and received fewer than 14,000. In 2008, Beijing anticipated more than 400,000 foreign guests and received 235,000 for the whole month of August.

The average number of hotel beds occupied in Beijing during the Olympics was 39% down on the previous year, the ETOA report showed. It said that while the Beijing Games may have been a "triumph of planning and showmanship", for the tourism industry they were a "toxic event that crushed normal demand, both business and leisure". The report said that while tourism chiefs and organisers had recognised that the Olympics would create some displacement, with visitors arriving for the games replacing those put off by the fact it was taking place, they still tended to talk in terms of a large overall boost.

"For London many in the industry are anticipating a boom, with up to 350,000 foreign visitors predicted per day during the Olympics," it said. "This expectation of bounty creates its own problems. In London, hoteliers expect to be full with premium business, and some anticipate a displacement of demand that fills up the surrounding months."

Lord Coe, chairman of the London Organising Committee of the Olympic Games, has talked of 1 million "extra" visitors coming to the UK for the games.

But the ETOA report claimed that the perception that the host city would be crowded and prices expensive was likely to tarnish the view of the country as a whole.

It said its members were already dealing with the perception that the UK would be crowded and so best avoided in 2012.

"The problem is not restricted to the host city. London is the gateway to the UK and its biggest draw. If you remove London from a visit to the British Isles, everywhere else becomes far more difficult to sell," it said. "Athens has nothing like the central importance that London occupies, yet when its visitor arrivals dropped by 6% in the Olympic year, regional Greece fell by 11%."

Olympic organisers and the mayor of London, Boris Johnson, face an ongoing battle to convince overseas travellers that visiting London for the games will remain cost-efficient and have appealed to hotels not to try and cash in by increasing their prices.

They would also argue that a narrow analysis of the number of people visiting during Games-time ignores its longer term benefits in terms of acting as a giant global marketing event for London and the UK and changing the perceptions of those who might not otherwise visit the country.

"Precisely because London is one of the top international destinations, it has more to lose. At the moment a false expectation of bookings is in danger of destroying an export industry," said the ETOA executive director, Tom Jenkins. "For August 2012, ETOA members – who alone regularly deliver over 15,000 hotel rooms per day – cannot reserve space. Without any reservations to sell, nothing can be sold."

A spokesman for the Department of Culture, Media and Sport said: "This is a weary old story. No one seriously believes that any tourist accommodation will remain unfilled during the Games themselves. The important point is that the 2012 Olympic and Paralympic Games are a long-term investment in the future of Britain's visitor economy and a once-in-a-lifetime opportunity to enhance the image of the UK as a visitor destination."

He added: "VisitBritain's marketing strategy and the creation of the new £1bn marketing and PR fund will be used to reassure the world that Britain is open for business throughout 2012. And showing the best that Britain has to offer while the spotlight of the world is upon us will create a tourism legacy for years to come."

Jenkins said that if politicians and tourism chiefs recognised the issues, they could plan to overcome them.

"Even during the peak moments the numbers attending the games themselves are unlikely to exceed those who attend games across the city during the football season. And these numbers are dwarfed by the millions of commuters that regularly use its infrastructure," he added "If this applies to the 17 days of an Olympics, then the message for the remaining 50 weeks is that London will be open, like no other city, for normal business. It is with this message that London must welcome the world."